From 6a3cd3318ff65622415e34e8ee39d76331e7c869 Mon Sep 17 00:00:00 2001 From: Dave Marchevsky Date: Sun, 12 Feb 2023 01:27:07 -0800 Subject: bpf: Migrate release_on_unlock logic to non-owning ref semantics This patch introduces non-owning reference semantics to the verifier, specifically linked_list API kfunc handling. release_on_unlock logic for refs is refactored - with small functional changes - to implement these semantics, and bpf_list_push_{front,back} are migrated to use them. When a list node is pushed to a list, the program still has a pointer to the node: n = bpf_obj_new(typeof(*n)); bpf_spin_lock(&l); bpf_list_push_back(&l, n); /* n still points to the just-added node */ bpf_spin_unlock(&l); What the verifier considers n to be after the push, and thus what can be done with n, are changed by this patch. Common properties both before/after this patch: * After push, n is only a valid reference to the node until end of critical section * After push, n cannot be pushed to any list * After push, the program can read the node's fields using n Before: * After push, n retains the ref_obj_id which it received on bpf_obj_new, but the associated bpf_reference_state's release_on_unlock field is set to true * release_on_unlock field and associated logic is used to implement "n is only a valid ref until end of critical section" * After push, n cannot be written to, the node must be removed from the list before writing to its fields * After push, n is marked PTR_UNTRUSTED After: * After push, n's ref is released and ref_obj_id set to 0. NON_OWN_REF type flag is added to reg's type, indicating that it's a non-owning reference. * NON_OWN_REF flag and logic is used to implement "n is only a valid ref until end of critical section" * n can be written to (except for special fields e.g. bpf_list_node, timer, ...) Summary of specific implementation changes to achieve the above: * release_on_unlock field, ref_set_release_on_unlock helper, and logic to "release on unlock" based on that field are removed * The anonymous active_lock struct used by bpf_verifier_state is pulled out into a named struct bpf_active_lock. * NON_OWN_REF type flag is introduced along with verifier logic changes to handle non-owning refs * Helpers are added to use NON_OWN_REF flag to implement non-owning ref semantics as described above * invalidate_non_owning_refs - helper to clobber all non-owning refs matching a particular bpf_active_lock identity. Replaces release_on_unlock logic in process_spin_lock. * ref_set_non_owning - set NON_OWN_REF type flag after doing some sanity checking * ref_convert_owning_non_owning - convert owning reference w/ specified ref_obj_id to non-owning references. Set NON_OWN_REF flag for each reg with that ref_obj_id and 0-out its ref_obj_id * Update linked_list selftests to account for minor semantic differences introduced by this patch * Writes to a release_on_unlock node ref are not allowed, while writes to non-owning reference pointees are. As a result the linked_list "write after push" failure tests are no longer scenarios that should fail. * The test##missing_lock##op and test##incorrect_lock##op macro-generated failure tests need to have a valid node argument in order to have the same error output as before. Otherwise verification will fail early and the expected error output won't be seen. Signed-off-by: Dave Marchevsky Link: https://lore.kernel.org/r/20230212092715.1422619-2-davemarchevsky@fb.com Signed-off-by: Alexei Starovoitov --- include/linux/bpf.h | 6 ++++++ include/linux/bpf_verifier.h | 38 ++++++++++++++++++-------------------- 2 files changed, 24 insertions(+), 20 deletions(-) (limited to 'include/linux') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 4385418118f6..8b5d0b4c4ada 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -181,6 +181,7 @@ enum btf_field_type { BPF_KPTR = BPF_KPTR_UNREF | BPF_KPTR_REF, BPF_LIST_HEAD = (1 << 4), BPF_LIST_NODE = (1 << 5), + BPF_GRAPH_NODE_OR_ROOT = BPF_LIST_NODE | BPF_LIST_HEAD, }; struct btf_field_kptr { @@ -576,6 +577,11 @@ enum bpf_type_flag { /* MEM is tagged with rcu and memory access needs rcu_read_lock protection. */ MEM_RCU = BIT(13 + BPF_BASE_TYPE_BITS), + /* Used to tag PTR_TO_BTF_ID | MEM_ALLOC references which are non-owning. + * Currently only valid for linked-list and rbtree nodes. + */ + NON_OWN_REF = BIT(14 + BPF_BASE_TYPE_BITS), + __BPF_TYPE_FLAG_MAX, __BPF_TYPE_LAST_FLAG = __BPF_TYPE_FLAG_MAX - 1, }; diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index aa83de1fe755..cf1bb1cf4a7b 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -43,6 +43,22 @@ enum bpf_reg_liveness { REG_LIVE_DONE = 0x8, /* liveness won't be updating this register anymore */ }; +/* For every reg representing a map value or allocated object pointer, + * we consider the tuple of (ptr, id) for them to be unique in verifier + * context and conside them to not alias each other for the purposes of + * tracking lock state. + */ +struct bpf_active_lock { + /* This can either be reg->map_ptr or reg->btf. If ptr is NULL, + * there's no active lock held, and other fields have no + * meaning. If non-NULL, it indicates that a lock is held and + * id member has the reg->id of the register which can be >= 0. + */ + void *ptr; + /* This will be reg->id */ + u32 id; +}; + struct bpf_reg_state { /* Ordering of fields matters. See states_equal() */ enum bpf_reg_type type; @@ -226,11 +242,6 @@ struct bpf_reference_state { * exiting a callback function. */ int callback_ref; - /* Mark the reference state to release the registers sharing the same id - * on bpf_spin_unlock (for nodes that we will lose ownership to but are - * safe to access inside the critical section). - */ - bool release_on_unlock; }; /* state of the program: @@ -331,21 +342,8 @@ struct bpf_verifier_state { u32 branches; u32 insn_idx; u32 curframe; - /* For every reg representing a map value or allocated object pointer, - * we consider the tuple of (ptr, id) for them to be unique in verifier - * context and conside them to not alias each other for the purposes of - * tracking lock state. - */ - struct { - /* This can either be reg->map_ptr or reg->btf. If ptr is NULL, - * there's no active lock held, and other fields have no - * meaning. If non-NULL, it indicates that a lock is held and - * id member has the reg->id of the register which can be >= 0. - */ - void *ptr; - /* This will be reg->id */ - u32 id; - } active_lock; + + struct bpf_active_lock active_lock; bool speculative; bool active_rcu_lock; -- cgit